Video viewing devices are in common use for a wide variety of applications. Cathode ray tube ("CRT") displays have long been used for television viewing, and more recently as computer monitors. More compact devices for viewing video images, such as liquid crystal display ("LCD") screens, have been developed as a substitute for CRT displays.
More recently compact, lightweight head mounted displays have been introduced as viewing devices for "virtual reality" systems. By providing a separate viewing device for each eye and appropriately varying the image viewable though each device, high-resolution stereographic video images may be displayed.
Another type of viewing device for video images are "heads up displays" ("HUD's") that enable jet fighter pilots to process mentally a huge amount of information pertaining to both the space surrounding the aircraft and the condition and performance of the aircraft. This has led to the development of HUD's built into the transparent canopy of aircraft, as well as "head-mounted displays" and "visor displays."
All of the above-described HUD's require light projected from a source display (such as a liquid crystal television screen) to travel some distance through air to a reflective, refractive or diffractive surface where the light is redirected to form a virtual image of the source display. A holographic optical element typically serves as a diffractive surface in such displays, and typically is highly color selective. However, it would be desirable to view a video image, particularly a three dimensional image, by directly generating a three-dimensional virtual image without the need for transmitting light from a source display through the air. If a technique could be found for avoiding the need to transmit light though the air over a substantial distance, the viewing device could be extremely compact, and could even closely resemble an ordinary pair of eyeglasses. The compact, lightweight and unobtrusive nature of such a viewing device would open up a multitude of new applications, such as allowing use as a monitor for a pocket-sized computer, a superior virtual reality viewing device, or as a prosthetic for deaf people to display visual cues derived from sound.